This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-108169, filed Apr. 10, 2000, the entire contents of which are incorporated herein by reference.
The present invention generally relates to a method and an apparatus for generating optically readable image data comprising dots which are printed on a printout medium. The present invention also relates to a computer-readable recording medium which stores programs including instructions for a computer to perform operations of such an image data generation apparatus.
Conventionally, as disclosed in U.S. Pat. No. 5,896,403 and U.S. Pat. No. Re 36,589, various technologies are developed and are already known for printing data including voices, images, and other types of information on a printout medium such as paper and the like in the form of optically readable dots.
FIG. 1 shows a plurality of adjacent virtual cells 200 virtually formed in a matrix on a printout medium. A partially enlarged view of these cells is shown at the left-bottom corner in FIG. 1.
Binary data 1 or 0 corresponds to presence or absence of an optically readable dot. A given dot is placed on a corresponding virtual cell and is printed on a printout medium. A special reader optically reads this printed dot to restore original binary data or reproduce a voice, for example.
The following describes this more specifically.
Data including voices, images, and other types of information is printed as an optically readable dot code 170 on a printout medium such as paper. The dot code 170 comprises a plurality of blocks 272.
Each block 272 comprises a data dot 282, a marker 174, and a block address 280. Data such as voice is divided into blocks each of which represents 1 or 0 as a data value. In a data area 180, the data dot 282 is placed as a black or white dot image according to a specified arrangement mode.
The marker 174 is used to find a reference point for detecting each data dot 282. The marker 174 is placed at four corners of each block 272 and comprises a specified number of consecutive black dots. The block address 280 is placed between markers 174 for identifying a plurality of different blocks 272 during reading. The block address 280 contains an error detection or correction sign.
In FIG. 1, a black dot is actually printed; no white dot is printed. A white dot corresponds to the ground color of a printout medium. A virtual cell is formed by virtual vertical and horizontal lines.
FIG. 2 is a functional block diagram of a reader for optically reading the dot code 170 by manual scanning.
As shown in FIG. 2, an output from a read unit 204 is connected to an input to a digitizing image memory 206 via a digitizing unit 205. An output from the digitizing image memory 206 is connected to an input to a reproduction unit 209 via a restoration unit 207 and a demodulation unit 208. The read unit 204 comprises an illumination unit 201, an optical system 202, and an image pickup unit 203. The illumination unit 201 comprises an LED and the like for illuminating the dot code 170. The optical system 202 forms an image using reflected light from the dot code 170. The image pickup unit 203 comprises an area sensor such as CCD and the like for picking imaging light from the optical system 202.
The read unit 204 reads an image comprising dot codes. The digitizing unit 205 digitizes an imaging signal output from the read unit 204 according to a specified digitizing threshold value.
The digitizing image memory 206 stores the image data digitized in the digitizing unit 205.
The restoration unit 207 reads the digitized image data stored in the digitizing image memory 206 and detects the dots. The restoration unit 207 allocates a value of 1 or 0 to each of the detected dots and outputs the data.
The demodulation unit 208 demodulates data output from the restoration unit 207. The reproduction unit 209 performs error correction using the Reed-Solomon code or the like and, for example, expands the error-corrected data for reproducing original data such as voices.
In this configuration, the restoration unit 207 reads the digitized image data stored in the digitizing image memory 206. When detecting each dot, the restoration unit 207 finds the marker 174 from the digitized image data. The restoration unit 207 then finds a dot read reference position based on the centroid position of the marker 174.
Based on the corresponding dot read reference position, the restoration unit 207 detects a dot read point for reading each data dot 282 in the data area 180. The restoration unit 207 determines whether the detected data dot 282 is white or black. Based on this result, the restoration unit 207 allocates the value 1 or 0 to the data dot and outputs the data.
When the dot code 170 is printed, for example, input data to be printed such as voice is modulated beforehand. The demodulation unit 208 restores the modulated data to the original data before modulation.
The restoration unit 207 previously performs this modulation for easily finding the marker 174 first. The modulation is applied to the input data such as voice so that the number of consecutive black dots becomes smaller in the data dot 282 than in the marker 174. The modulation is performed for making a distinction between each data dot 282 and the marker 174 in the data area 180.
For printing the above-mentioned dot code 170, an image processing system such as a computer or a workstation is used to create image data for dot codes by processing information to be recorded. The corresponding image data is output to a typesetting device such as an imagesetter to create an image set copy. Thus, the dot code 170 is finally printed.
The following describes a system configuration for printing the dot code 170 with reference to FIG. 3A. In FIG. 3A, voice or image information to be dot-coded is input to a computer from an input device 100.
The computer 102 references a data compression system, an error correction system, format information of the dot code 170 and the like stored in an external storage device 104. The input signal is converted to image information to be output to an imagesetter 106. This image information is supplied to the imagesetter 106. The dot code 170 is then imaged on a film. A typesetting exposure device 108 exposes this film onto an image set copy. The thus created image set copy is printed from a printer 110 to create a printout which records the dot code 170 in a printed form.
FIG. 3B shows a device which can directly create an image set copy without imaging on films.
When the virtual cell is virtually formed on paper, the virtual cell size depends on a resolution specific to a typesetting device (imagesetter) to be used actually. When a specified virtual cell comprises a plurality of pixels, dot image data needs to be created for determining how many pixels should be associated with actual dot printing. It is also known that creation of the dot image data needs to consider enlargement of the corresponding dot (hereafter referred to as the dot gain) when it is actually printed on paper.
These items are already proposed by the applicant in U.S. Pat. No. 6,014,501. The following describes them in detail with reference to FIG. 4.
FIG. 4 shows a reference table for defining a composition pattern of pixels constituting dot image data according to a dot gain. The dot gain depends on an imagesetter resolution and characteristics of a printer, paper, and ink to be used actually. As disclosed in U.S. Pat. No. 6,014,501, a dot to be printed may occupy approximately 50% to 80% of one virtual cell including the dot enlargement.
Conditions of easily enlarging dots include a rotary press printer for fast printing on both sides of paper, easily bleeding rough paper, and less viscous ink. When dots easily enlarge, namely the dot gain is large, a composition pattern should contain few pixels associated with printing (rightmost xe2x80x9clargexe2x80x9d or xe2x80x9cextra-largexe2x80x9d in FIG. 4).
Conditions of preventing dots from enlarging include a sheet-fed press printer, hardly bleeding paper such as high-quality coated paper, and more viscous ink. When dots hardly enlarge, namely the dot gain is small, a composition pattern should contain many pixels associated with printing (leftmost xe2x80x9csmallxe2x80x9d in FIG. 4).
FIG. 4 shows an example of creating dot image data at a dot pitch of approximately 60 xcexcm. This example uses imagesetter resolutions of 2400 dpi, 2540 dpi, and 3000 dpi. At 2400 dpi, one pixel is sized 10.6 xcexcm. To approximate 60 xcexcm, 6 pixels are used to create a dot pitch of 63.5 xcexcm. At 2540 dpi, one pixel is sized 10 xcexcm. Just 6 pixels are used to create a dot pitch of 60 xcexcm. At 3000 dpi, one pixel is sized 8.5 xcexcm. To approximate 60 xcexcm, 7 pixels are used to create a dot pitch of 59.3 xcexcm.
A circle is an ideal shape for a composition pattern of pixels constituting dot image data. However, it is difficult to form an ideal circle unless the resolution is extremely high. Accordingly, as shown in FIG. 4, an actual composition pattern forms a square (S for square) comprising 4 by 4, 5 by 5, or 6 by 6 pixels. Alternatively, it forms a rounded square (c for circle) by eliminating four corners from the corresponding square.
In the course of operations based on the above-mentioned principle, the dot image data generation method disclosed in U.S. Pat. No. 6,014,501 causes the following problems.
FIGS. 5A through 6C show composition patterns of pixels for 1-dot image data placed in one virtual cell when an imagesetter at 1200 dpi is used for creating an image set copy of dot codes. One pixel at 1200 dpi provides a pitch of 21.6 xcexcm. To provide a dot pitch approximate to 60 xcexcm, it is necessary to use 3 pixels to create a dot pitch of 63.5 xcexcm.
According to the technique disclosed in the above-mentioned U.S. Pat. No. 6,014,501, there are provided three patterns in FIGS. 5A through 5C in order to form a dot image data shape approximate to a square or a circle.
As the experiment proceeds, however, it has become apparent that none of the patterns in FIGS. 5A through 5C provides an appropriate number of pixels associated with printing based on the principle that dot enlargement should be considered for setting dot image data.
Namely, when dot printing is associated with 1 pixel (FIG. 5A), the printed dot is too fine. When dot printing is associated with 4 pixels (FIG. 5B) or 5 pixels (FIG. 5C), the printed dot is too thick.
As an experiment result, it has become apparent that 3 pixels are optimal for dot printout. When dot printing is associated with 3 pixels, there are three possible patterns as shown in FIGS. 6A through 6C. None of these composition patterns provides a shape approximate to a square or circle.
Accordingly, the technique disclosed in U.S. Pat. No. 6,014,501, alone could not select an optimal composition pattern. It may be possible to determine the number of pixels to be associated with printing out of a plurality of pixels which constitutes one virtual cell in the dot image data. Nevertheless, there may be provided a plurality of dot composition patterns each of which comprises the same number of pixels. There arises a new problem that it is further necessary to determine which composition pattern should be selected.
The present invention has been made in consideration of the foregoing. It is therefore an object of the present invention to provide a method and an apparatus for generating optically readable dot image data and a recording medium, in which it is possible to select an optimal composition pattern out of a plurality of composition patterns for dot image data based on the number of pixels associated with printing even if a plurality of pixels constitutes a virtual cell for single dot image data and the virtual cell contains the specified number of pixels associated with actual printout of a single dot.
To achieve the above-mentioned purpose, a first mode of the present invention provides a method for generating optically readable dot image data when binary data corresponds to presence or absence of an optically readable dot and the dot is printed in a virtual cell virtually formed on a printout medium, comprising: a first step of determining the number of pixels constituting the virtual cell as a minimum print unit in a typesetting device used for printing the dot on a printout medium; a second step of determining the number of pixels in the virtual cell associated with printout of the dot in consideration of enlargement of the dot when printed on a printout medium based on the dot image data; and a third step of selecting a composition pattern which minimizes dispersion of pixels constituting the dot image data when a plurality of composition patterns is available as composition patterns for dot image data comprising the number of pixels determined by the second step.
A second mode there of provides an apparatus for generating optically readable dot image data when binary data corresponds to presence or absence of an optically readable dot and the dot is printed in a virtual cell virtually formed on a printout medium, comprising: first means for determining the number of pixels constituting the virtual cell as a minimum print unit in a typesetting device used for printing the dot on a printout medium; second means for determining the number of pixels in the virtual cell associated with printout of the dot in consideration of enlargement of the dot when printed on a printout medium based on the dot image data; and third means for selecting a composition pattern which minimizes dispersion of pixels constituting the dot image data when a plurality of composition patterns is available as composition patterns for dot image data comprising the number of pixels determined by the second means.
In order to generate optically readable dot image data when binary data corresponds to presence or absence of an optically readable dot and the dot is printed in a virtual cell virtually formed on a printout medium, a third mode thereof provides a computer-readable recording medium which stores programs including instructions for a computer to perform: a first process for determining the number of pixels constituting the virtual cell as a minimum print unit in a typesetting device used for printing the dot on a printout medium; a second process for determining the number of pixels in the virtual cell associated with printout of the dot in consideration of enlargement of the dot when printed on a printout medium based on the dot image data; and a third process for selecting a composition pattern which minimizes dispersion of pixels constituting the dot image data when a plurality of composition patterns is available as composition patterns for dot image data comprising the number of pixels determined by the second process.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.